Due to the nonideality of a high pressure hydrogen release the possibility of a two-phase flow and its effect on the dynamics of the discharge process was experimentally investigated. A small-scale facility was designed and constructed to simulate the transient blow-down of a cryogenic fluid through a small break. Gaseous and liquid nitrogen were planned to were used as a surrogate for GH2 and LH2. The results will complement the quasi-stationary safety regulation tests and will provide time-dependent data for verification of the theoretical models. Different orifice sizes (0.5, 1, 2, 4 mm) and initial N2 pressures (30 ? 200 bar) were used in the tests. The measured time-dependent data for vessel discharge pressure, thrust, discharge mass flow rate, and gas temperatures were compared against a theoretical model for high pressure nitrogen release. This verification for nitrogen also assures the equation of state for hydrogen, which is based on the same methodology.